Methods For Non-Isothermal Wet Atomic Layer Etching

ABSTRACT

The present disclosure provides a non-isothermal wet atomic layer etch (ALE) process for etching polycrystalline materials, such as metals, metal oxides and silicon-based materials, formed on a substrate. More specifically, the present disclosure provides various embodiments of methods that utilize thermal cycling in a wet ALE process to independently optimize the reaction temperatures utilized within individual processing steps of the wet ALE process. Like conventional wet ALE processes, the wet ALE process described herein is a cyclic process that includes multiple cycles of surface modification and dissolution steps. Unlike conventional wet ALE processes, however, the wet ALE process described herein is a non-isothermal process that performs the surface modification and dissolution steps at different temperatures. This allows independent optimization of the surface modification and dissolution reactions.

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 17/674,579, filed Feb. 17, 2022, entitled “Methodsfor Wet Atomic Layer Etching of Ruthenium,” which claims priority toU.S. Provisional Patent Application Ser. No. 63/257,226, filed Oct. 19,2021, entitled “METHOD FOR WET ATOMIC LAYER ETCHING OF RUTHENIUM”; thedisclosure of which is expressly incorporated herein, in its entirety,by reference.

This application is related to co-pending, commonly owned U.S. patentapplication Ser. No. 17/725,072, filed Apr. 20, 2022, entitled “Methodsfor Wet Atomic Layer Etching of Copper,” the disclosure of which isexpressly incorporated herein, in its entirety, by reference.

BACKGROUND

This disclosure relates to semiconductor device manufacturing, and, inparticular, to the removal and etching of polycrystalline materials,such as metals, formed on a substrate. More specifically, the disclosurerelates to the process of wet atomic layer etching (ALE) ofpolycrystalline materials.

During routine semiconductor fabrication, various metals formed on asubstrate may be removed by patterned etching, chemical-mechanicalpolishing, as well as other techniques. A variety of techniques areknown for etching layers on a substrate, including plasma-based or vaporphase etching (otherwise referred to as dry etching) and liquid basedetching (otherwise referred to as wet etching). Wet etching generallyinvolves dispensing a chemical solution over the surface of a substrateor immersing the substrate in the chemical solution. The chemicalsolution often contains a solvent, chemicals designed to react withmaterials on the substrate surface and chemicals to promote dissolutionof the reaction products. As a result of exposure of the substratesurface to the etchant, material is removed from the substrate. Etchantcomposition and temperature may be controlled to control the etch rate,specificity, and residual material on the surface of the substratepost-etch.

Thermodynamics and kinetics both play roles in etchant formulation. Thedesired reactions need to be both thermodynamically and kineticallyfavorable for a successful etch. The requirements for success becomemuch more stringent for etching polycrystalline materials. For thesematerials, it is desirable that the removal rates for each individualcrystallite facet and grain boundary geometry is substantially similarregardless of crystallite morphology or environment. Surface roughnessplays an important role in interface quality and electrical propertiesof nanoscale features. When etching nanoscale polycrystalline materials,differing etch rates at grain boundaries compared to the differentcrystal facets leads to roughening of the surface during etching.Further, it is desirable that the material removal rate should beuniform at the macroscopic and microscopic levels and occurs at a ratethat is compatible with high volume manufacturing. Macroscopicuniformity can be addressed with careful engineering, but microscopicuniformity depends on the chemistry of the etch itself.

As geometries of substrate structures continue to shrink and the typesof structures evolve, the challenges of etching substrates haveincreased. One technique that has been utilized to address thesechallenges is atomic layer etching (ALE). ALE is a process that removesthin layers sequentially through one or more self-limiting reactions.For example, ALE typically refers to techniques that can etch withatomic precision, i.e., by removing material one or a few monolayers ofmaterial at a time. ALE processes generally rely on a chemicalmodification of the surface to be etched followed by selective removalof the modified surface layer. Thus, ALE processes offer improvedperformance by decoupling the etch process into sequential steps ofsurface modification and selective removal of the modified surfacelayer. In some embodiments, an ALE process may include multiple cyclicseries of surface modification and etch steps, where the modificationstep modifies the exposed surfaces and the etch step selectively removesthe modified surface layer. In such processes, a series of self-limitingreactions may occur and the cycle may be repeatedly performed until adesired or specified etch amount is achieved. In other embodiments, anALE process may use just one cycle.

A variety of ALE processes are known in the art, including plasma ALE,thermal ALE and wet ALE techniques. Like all ALE processes, wet ALE istypically a cyclic process that uses sequential, self-limiting reactionsto chemically modify an exposed surface of a material to form a modifiedsurface layer and selectively remove the modified surface layer from thesurface. Unlike thermal and plasma ALE techniques, however, thereactions used in wet ALE primarily take place in the liquid phase.

For example, a wet ALE process may generally begin with a surfacemodification step, which exposes a material to be etched to a firstsolution to create a self-limiting modified surface layer. The modifiedsurface layer may be created through oxidation, reduction, ligandbinding, or ligand exchange. Ideally, the modified surface layer isconfined to the top monolayer of the material and acts as a passivationlayer to prevent the modification reaction from progressing any further.After the modified surface layer is formed, the wet ALE process mayexpose the modified surface layer to a second solution to selectivelydissolve the modified surface layer in a subsequent dissolution step.Ideally, the dissolution step will selectively dissolve the modifiedsurface layer without removing any of the underlying unmodifiedmaterial. This selectivity can be accomplished by using a differentsolvent in the dissolution step than was used in the surfacemodification step, changing the pH, or changing the concentration ofother components in the first solvent. The wet ALE cycle can be repeateduntil a desired or specified etch amount is achieved.

In conventional ALE processes, the surface modification and etch stepsare usually performed at the same temperature, resulting in anisothermal etch process. In conventional wet ALE processes, for example,the surface modification and dissolution steps are often performed at(or near) room temperature. This is usually considered to be anadvantage of wet ALE over other ALE techniques. In plasma and thermalALE processes, the surface modification and etch steps are oftenperformed at a higher temperature than is typically used for wet ALE.Like wet ALE, however, plasma and thermal ALE are typically isothermalprocesses. Because adjusting and reaching thermal equilibrium at eachcycle is too time-consuming, plasma and thermal ALE processes must beconducted isothermally to meet the throughput requirements of highvolume manufacturing.

SUMMARY

The present disclosure provides a non-isothermal wet atomic layer etch(ALE) process for etching polycrystalline materials, such as metals,metal oxides and silicon-based materials, formed on a substrate. Morespecifically, the present disclosure provides various embodiments ofmethods that utilize thermal cycling in a wet ALE process toindependently optimize the reaction temperatures utilized withinindividual processing steps of the wet ALE process. Like conventionalwet ALE processes, the wet ALE process described herein is a cyclicprocess that includes multiple cycles of surface modification anddissolution steps. Unlike conventional wet ALE processes, however, thewet ALE process described herein is a non-isothermal process thatperforms the surface modification and dissolution steps at differenttemperatures. This allows independent optimization of the surfacemodification and dissolution reactions.

The non-isothermal wet ALE process described herein may generallyinclude multiple ALE cycles, where each ALE cycle includes a surfacemodification step, a first purge step, a dissolution step and a secondpurge step, and where one or more of these processing steps is performedat a different temperature. In some embodiments, thermal cycling can beintroduced as part of the wet ALE process described herein by dispensingliquid solutions utilized within one or more of the processing steps ata different temperature. The high heat capacity of the liquid solutions,combined with their high convective heat transfer coefficients, allowsthe substrate surface to reach thermal equilibration quickly, thusallowing the temperature of the substrate to be changed within thetimescale of a single ALE cycle.

In some embodiments, the non-isothermal wet ALE process described hereinmay dispense a surface modification solution onto a surface of asubstrate at a first temperature, and may subsequently dispense adissolution solution onto the surface of the substrate at a secondtemperature, which is different from the first temperature. The firsttemperature and the second temperature may be selected to independentlyoptimize the reactions that occur during the surface modification anddissolution steps. In some embodiments, for example, the surfacemodification solution may be dispensed at a first temperature, which isless than or equal to room temperature (e.g., a temperature less than orequal to 25° C.). However, the dissolution solution may be dispensed ata second temperature, which is greater than room temperature (e.g., atemperature greater than or equal to 40° C.) to optimize the kinetics ofthe dissolution reaction. By utilizing liquid solutions havingsubstantially different temperatures, the wet ALE process describedherein provides a cyclic, non-isothermal etch process, which repeatedlyadjusts the reaction temperatures of the surface modification anddissolution steps to independently optimize the surface modification anddissolution reactions.

During each ALE cycle, purge solutions may be dispensed onto the surfaceof the substrate between the surface modification and dissolution stepsto remove the surface modification and dissolution solutions from thesurface of the substrate. In some embodiments, the purge solutions maybe utilized to pre-heat or pre-cool the substrate prior to performingthe next processing step. After performing a surface modification step,for example, a heated purge solution may be dispensed onto the surfaceof the substrate to bring the temperature of the substrate closer to thesecond temperature (i.e., the desired dissolution reaction temperature)prior to performing the next dissolution step. After the dissolutionstep is performed, a room temperature (or cooled) purge solution may bedispensed onto the surface of the substrate to bring the temperature ofthe substrate closer to the first temperature (i.e., the desired surfacemodification reaction temperature) prior to performing the next surfacemodification step. By using the temperature and thermal mass of thepurge solutions, the wet ALE process described herein is able to quicklyadjust the surface of the substrate to the next process temperature.

Accordingly, a cyclic, non-isothermal wet ALE process is disclosedherein for etching polycrystalline materials. By utilizing heated(and/or cooled) liquid solutions, the cyclic, non-isothermal wet ALEprocess described herein quickly adjusts the reaction temperatures ofthe surface modification and dissolution steps within the timescale of asingle ALE cycle to independently optimize the surface modification anddissolution reactions. The disclosed non-isothermal wet ALE process isable to change the substrate temperature, during processing, much easierand faster than can be achieved in the gas-phase processing used inplasma and thermal ALE. Accordingly, the disclosed non-isothermal wetALE process is suitable for high volume manufacturing.

As noted above and described further herein, the present disclosureprovides various embodiments of methods that utilize thermal cycling ina wet ALE process to independently optimize the reaction temperaturesutilized within the individual processing steps of the wet ALE process.Of course, the order of discussion of the different steps as describedherein has been presented for clarity sake. In general, these steps canbe performed in any suitable order. Additionally, although each of thedifferent features, techniques, configurations, etc. herein may bediscussed in different places of this disclosure, it is intended thateach of the concepts can be executed independently of each other or incombination with each other. Accordingly, the present invention can beembodied and viewed in many different ways.

According to one embodiment, a method is provided herein for etching apolycrystalline material using a non-isothermal wet atomic layer etching(ALE) process. The method may generally include receiving a substratehaving a polycrystalline material formed thereon, wherein a surface ofthe polycrystalline material is exposed on a surface of the substrate,and dispensing a surface modification solution onto the surface of thesubstrate at a first temperature, wherein the surface modificationsolution chemically modifies the surface of the polycrystalline materialto form a passivation layer on the surface of the polycrystallinematerial. Next, the method may include removing the surface modificationsolution from the surface of the substrate subsequent to forming thepassivation layer, and dispensing a dissolution solution onto thesurface of the substrate at a second temperature, which is differentfrom the first temperature, wherein the dissolution solution selectivelyremoves the passivation layer from the surface of the polycrystallinematerial. Next, the method may include removing the dissolution solutionfrom the surface of the substrate, and repeating the steps of dispensingthe surface modification solution, removing the surface modificationsolution, dispensing the dissolution solution, and removing thedissolution solution a number of ALE cycles until a predetermined amountof the polycrystalline material is removed from the substrate.

As noted above, the first temperature and the second temperature may beselected so as to independently optimize the reactions that occur duringthe surface modification and dissolution steps of the non-isothermal wetALE process described herein. In some embodiments, the surfacemodification solution may be dispensed within a first temperature rangehaving a lower limit that is set by the freezing point of the surfacemodification solution and an upper limit of approximately roomtemperature (e.g., a temperature ranging between 20° C. and 25° C.). Inone example embodiment, the surface modification solution may bedispensed at approximately room temperature (e.g., a temperature rangingbetween 20° C. and 25° C.). In some embodiments, the dissolutionsolution may be dispensed at a second temperature, which is greater thanthe first temperature to optimize the kinetics of the dissolutionreaction. For example, the dissolution solution may be dispensed withina second temperature range having a lower limit of 40° C. and an upperlimit that is set by the boiling point of the dissolution etch solution.In one example embodiment, the dissolution solution may be dispensedwithin a second temperature range comprising 40° C. to 337° C.

In some embodiments, said removing the surface modification solution mayinclude dispensing a first purge solution onto the surface of thesubstrate to remove the surface modification solution from the surfaceof the substrate prior to dispensing the dissolution solution. In someembodiments, a temperature of the first purge solution may bring atemperature of the substrate closer to the second temperature before thedissolution solution is dispensed. In some embodiments, the temperatureof the first purge solution may be within 10% of the second temperature.

In some embodiments, said removing the dissolution solution may includedispensing a second purge solution onto the surface of the substrate toremove the dissolution solution from the surface of the substrate beforere-dispensing the surface modification solution during a subsequent ALEcycle. In some embodiments, a temperature of the second purge solutionmay bring a temperature of the substrate closer to the first temperaturebefore the surface modification solution is re-dispensed during thesubsequent ALE cycle. In some embodiments, the temperature of the secondpurge solution may be within 10% of the first temperature.

Different etch chemistries may be used within the surface modificationand the dissolution solutions for etching a wide variety ofpolycrystalline materials, such as metals, metal oxides silicon-basedmaterials. Examples of metals that may be etched using the methodsdisclosed herein include, but are not limited to, ruthenium (Ru), cobalt(Co), copper (Cu), molybdenum (Mo), tungsten (W), gold (Au), platinum(Pt), iridium (Ir) and other transition metals. Example of metal oxidesthat may be etched using the methods disclosed herein include, but arenot limited to, aluminum oxide (Al₂O₃), hafnium oxide (HfO₂). In someembodiments, the methods disclosed herein may also be used to etchsilicon-based materials, such as but not limited to, silicon (Si),silicon oxides (e.g., SiO and SiO₂) and silicon nitrides (e.g., Si₃N₄).Although various examples are provided herein, one skilled in the artwould recognize how the methods disclosed herein may be used to etchother metals, metal oxides and silicon-based materials. Example etchchemistries for etching ruthenium and molybdenum using thenon-isothermal wet ALE techniques disclosed herein are discussed in moredetail below.

In some embodiments, the method disclosed herein may be used for etchinga ruthenium (Ru) surface. When the method disclosed herein is utilizedfor etching a ruthenium surface, the surface modification solution mayinclude a halogenation agent (e.g., a chlorination agent, a fluorinatingagent or a brominating agent) dissolved in a first solvent, and thedissolution solution may include a ligand dissolved in a second solvent.The halogenation agent included within the surface modification solutionchemically modifies the ruthenium surface to form a halogenatedruthenium passivation layer. The ligand included within the dissolutionsolution reacts with and binds to the halogenated ruthenium passivationlayer to form a soluble species, which is dissolved within the secondsolvent to selectively remove the halogenated ruthenium passivationlayer from the ruthenium surface. In some embodiments, the surfacemodification solution may be dispensed at a first temperature rangingbetween 20° C. and 25° C., and the dissolution solution may be dispensedat a second temperature ranging between 40° C. and 100° C.

In other embodiments, the method disclosed herein may be used foretching a molybdenum (Mo) surface. When the method disclosed herein isutilized for etching a molybdenum surface, the surface modificationsolution may include an oxidation agent and a first ligand dissolved ina first solvent, and the dissolution solution may include a secondligand dissolved in a second solvent. The oxidation agent oxidizes themolybdenum surface to form a molybdenum oxide passivation layer. Thefirst ligand included within the surface modification solution reactswith and binds to the molybdenum oxide passivation layer to form aligand-metal complex, which is insoluble in the first solvent. Whenexposed to the dissolution solution, a ligand exchange process exchangesthe first ligand in the ligand-metal complex with the second ligandincluded within the dissolution solution to form a soluble species,which is dissolved within the second solvent to selectively remove themolybdenum oxide passivation layer from the molybdenum surface. In someembodiments, the surface modification solution may be dispensed at afirst temperature ranging between 20° C. and 25° C., and the dissolutionsolution may be dispensed at a second temperature ranging between 40° C.and 337° C.

According to another embodiment, a method is provided herein for etchinga substrate using a non-isothermal wet atomic layer etching (ALE)process. The method may generally include: a) receiving the substrate,the substrate having a ruthenium surface exposed thereon; b) exposingthe ruthenium surface to a first etch solution containing a halogenatingagent to chemically modify the ruthenium surface and form a rutheniumhalide passivation layer, wherein the first etch solution is dispensedonto a surface of the substrate at a first temperature; c) rinsing thesubstrate with a first purge solution to remove the first etch solutionfrom the surface of the substrate; d) exposing the ruthenium halidepassivation layer to a second etch solution to selectively remove theruthenium halide passivation layer without removing the rutheniumsurface underlying the ruthenium halide passivation layer, wherein thesecond etch solution is dispensed onto the surface of the substrate at asecond temperature, which is greater than the first temperature; e)rinsing the substrate with a second purge solution to remove the secondetch solution from the surface of the substrate; and f) repeating stepsb)-e) for one or more cycles.

In some embodiments, the first etch solution may be dispensed onto thesurface of the substrate at a first temperature, which is less than orapproximately equal to room temperature. In one example, the firsttemperature may be selected from a first temperature range comprising20° C. to 25° C. Although the example provided is within roomtemperature range, the first temperature is not strictly limited tosuch, and may alternatively range between an upper limit of 25° C. and alower limit that is set by the freezing point of the first etchsolution. As noted above, the second etch solution may be dispensed ontothe surface of the substrate at a second temperature, which is greaterthan the first temperature to optimize the kinetics of the dissolutionreaction. In one example, the second temperature may be selected from asecond temperature range comprising 40° C. to 100° C. Like the firsttemperature, however, the second temperature is not strictly limited tosuch a temperature range, and may comprise any elevated temperature thatis greater than room temperature and less than the boiling point of thesecond etch solution. For example, the second temperature may rangebetween a lower limit of 40° C. and an upper limit that is set by theboiling point of the second etch solution.

In some embodiments, the first etch solution may include a chlorinationagent dissolved in a first solvent. In such embodiments, thechlorination agent may react with the ruthenium surface to form aruthenium chloride passivation layer, which is insoluble in the firstsolvent. For example, the chlorination agent may includetrichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride orN-chlorosuccinimide, and the first solvent may include ethyl acetate(EA), acetone, acetonitrile, or a chlorocarbon.

In some embodiments, the second etch solution may include a liganddissolved in a second solvent. In such embodiments, the ligand may reactwith and bind to the ruthenium chloride passivation layer to form asoluble species that dissolves within the second solvent. For example,the ligand may include ethylenediaminetetraacetic acid (EDTA),iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA) oracetylacetone (ACAC), and the second solvent may include a base.

Note that this summary section does not specify every embodiment and/orincrementally novel aspect of the present disclosure or claimedinvention. Instead, this summary only provides a preliminary discussionof different embodiments and corresponding points of novelty overconventional techniques. For additional details and/or possibleperspectives of the invention and embodiments, the reader is directed tothe Detailed Description section and corresponding figures of thepresent disclosure as further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present inventions and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features. It is to be noted, however, that theaccompanying drawings illustrate only exemplary embodiments of thedisclosed concepts and are therefore not to be considered limiting ofthe scope, for the disclosed concepts may admit to other equallyeffective embodiments.

FIG. 1 illustrates one example of a cyclic, non-isothermal wet atomiclayer etching (ALE) process that can be used to etch ruthenium inaccordance with the present disclosure.

FIG. 2 is a graph depicting exemplary etch amounts (expressed innanometers, nm) that may be achieved as a function of cycle number whenattempting to etch ruthenium using various etch conditions.

FIG. 3 is a graph illustrating how the temperature of the individualprocess steps of the non-isothermal wet ALE process may be adjustedduring each ALE cycle.

FIG. 4 illustrates one example of a cyclic, non-isothermal wet atomiclayer etching (ALE) process that can be used to etch molybdenum inaccordance with the present disclosure.

FIG. 5 is a graph illustrating how the oxidation of the molybdenumsurface using hydrogen peroxide (H₂O₂) and oxalic acid in isopropylalcohol (IPA) to form oxymolybdenum oxalate is self-limiting at roomtemperature, but not self-limiting at elevated temperatures.

FIG. 6 is a graph depicting exemplary etch amounts (expressed innanometers, nm) that may be achieved as a function of cycle number whenattempting to etch molybdenum using various etch conditions.

FIG. 7 is a block diagram of an example processing system that can usethe techniques described herein to etch a polycrystalline material, suchas ruthenium.

FIG. 8 is a flowchart diagram illustrating one embodiment of a methodutilizing the techniques described herein.

FIG. 9 is a flowchart diagram illustrating another embodiment of amethod utilizing the techniques described herein.

DETAILED DESCRIPTION

As noted above, conventional methods for etching polycrystallinematerials are typically conducted as isothermal processes. For example,most wet ALE processes developed thus far are run isothermally at roomtemperature. Although plasma and thermal ALE processes may be performedat higher temperatures than is typically used for wet ALE, plasma andthermal ALE processes must be run isothermally to meet the throughputrequirements of high volume manufacturing.

The present inventors recognized that, in some ALE processes, one of thereaction steps may benefit from being run at a higher temperature. Forexample, the present inventors recognized that increasing thetemperature of the dissolution reaction may improve the kinetics ofdissolution and increase the etch rate when etching some materials.However, the present inventors noted that raising the temperature forthe benefit of one reaction is sometimes detrimental to the secondreaction. As such, the present inventors recognized that it is notalways desirable to run the entire process at an elevated temperature,and developed a non-isothermal etch process that improves uponconventional etch processes run isothermally.

In the present disclosure, a non-isothermal wet atomic layer etch (ALE)process is provided for etching polycrystalline materials, such asmetals, metal oxides and silicon-based materials, formed on a substrate.More specifically, the present disclosure provides various embodimentsof methods that utilize thermal cycling in a wet ALE process toindependently optimize the reaction temperatures utilized withinindividual processing steps of the wet ALE process. Like conventionalwet ALE processes, the wet ALE process described herein is a cyclicprocess that includes multiple cycles of surface modification anddissolution steps. Unlike conventional wet ALE processes, however, thewet ALE process described herein is a non-isothermal process thatperforms the surface modification and dissolution steps at differenttemperatures. This allows independent optimization of the surfacemodification and dissolution reactions.

The non-isothermal wet ALE process described herein may generallyinclude multiple ALE cycles, where each ALE cycle includes a surfacemodification step, a first purge step, a dissolution step and a secondpurge step, and where one or more of these processing steps is performedat a different temperature. In some embodiments, thermal cycling can beintroduced as part of the wet ALE process described herein by dispensingliquid solutions utilized within one or more of the processing steps ata different temperature. The high heat capacity of the liquid solutions,combined with their high convective heat transfer coefficients, allowsthe substrate surface to reach thermal equilibration quickly, thusallowing the temperature of the substrate to be changed within thetimescale of a single ALE cycle.

In some embodiments, the non-isothermal wet ALE process described hereinmay dispense a surface modification solution onto a surface of asubstrate at a first temperature, and may subsequently dispense adissolution solution onto the surface of the substrate at a secondtemperature, which is different from the first temperature. The firsttemperature and the second temperature may be selected to independentlyoptimize the reactions that occur during the surface modification anddissolution steps. In some embodiments, for example, the surfacemodification solution may be dispensed at a first temperature, which isless than or equal to room temperature (e.g., a temperature less than orequal to 25° C.). However, the dissolution solution may be dispensed ata second temperature, which is greater than room temperature (e.g., atemperature greater than or equal to 40° C.) to optimize the kinetics ofthe dissolution reaction. By utilizing liquid solutions havingsubstantially different temperatures, the wet ALE process describedherein provides a cyclic, non-isothermal etch process, which repeatedlyadjusts the reaction temperatures of the surface modification anddissolution steps to independently optimize the surface modification anddissolution reactions.

During each ALE cycle, purge solutions may be dispensed onto the surfaceof the substrate between the surface modification and dissolution stepsto remove the surface modification and dissolution solutions from thesurface of the substrate. In some embodiments, the purge solutions maybe utilized to pre-heat or pre-cool the substrate prior to performingthe next processing step. After performing a surface modification step,for example, a heated purge solution may be dispensed onto the surfaceof the substrate to bring the temperature of the substrate closer to thesecond temperature (i.e., the desired dissolution reaction temperature)prior to performing the next dissolution step. After the dissolutionstep is performed, a room temperature (or cooled) purge solution may bedispensed onto the surface of the substrate to bring the temperature ofthe substrate closer to the first temperature (i.e., the desired surfacemodification reaction temperature) prior to performing the next surfacemodification step. By using the temperature and thermal mass of thepurge solutions, the wet ALE process described herein is able to quicklyadjust the surface of the substrate to the next process temperature.

The techniques described herein offer multiple advantages overconventional methods by providing a cyclic, non-isothermal wet ALEprocess for etching polycrystalline materials, such as metals. As notedabove, thermal cycling is used in the wet ALE process described hereinto independently optimize the reaction temperatures utilized within thesurface modification and dissolution steps of the wet ALE process. Inparticular, thermal cycling is provided by utilizing heated (and/orcooled) liquid solutions, which quickly adjusts the reactiontemperatures of the surface modification and dissolution steps withinthe timescale of a single ALE cycle to independently optimize thesurface modification and dissolution reactions. Unlike some conventionaletch processes, the cyclic, non-isothermal wet ALE process describedherein is able to quickly change the substrate temperature duringprocessing, and thus, is suitable for high volume manufacturing.

The techniques described herein may be used for etching a wide varietyof polycrystalline materials, such as metals, metal oxides andsilicon-based materials. Examples of metals that may be etched using themethods disclosed herein include, but are not limited to, ruthenium(Ru), cobalt (Co), copper (Cu), molybdenum (Mo), tungsten (W), gold(Au), platinum (Pt), iridium (Ir) and other transition metals. Exampleof metal oxides that may be etched using the methods disclosed hereininclude, but are not limited to, aluminum oxide (Al₂O₃), hafnium oxide(HfO₂). In some embodiments, the methods disclosed herein may also beused to etch silicon-based materials, such as but not limited to,silicon (Si), silicon oxides (e.g., SiO and SiO₂) and silicon nitrides(e.g., Si₃N₄). Although various examples are provided herein, oneskilled in the art would recognize how the methods disclosed herein maybe used to etch other metals, metal oxides and silicon-based materials.Example etch processes and etch chemistries for etching ruthenium andmolybdenum are discussed in more detail below.

FIG. 1 illustrates one example of a cyclic, non-isothermal wet ALEprocess in accordance with the present disclosure. More specifically,FIG. 1 illustrates exemplary steps performed during one cycle of anon-isothermal wet ALE process used for etching a polycrystallinematerial 105, such as ruthenium (Ru). In the process shown in FIG. 1 , apolycrystalline material 105 surrounded by a dielectric material 110 isbrought in contact with a surface modification solution 115 during asurface modification step 100 to modify exposed surfaces of thepolycrystalline material 105. In one embodiment, the polycrystallinematerial 105 to be etched may be ruthenium (Ru). When etching ruthenium,the surface modification solution 115 may contain a halogenation agent120. For example, the surface modification solution 115 may include afirst solvent containing a chlorination agent, a fluorinating agent or abrominating agent.

As shown in FIG. 1 , a chemical reaction occurs at the exposed surfaceof the polycrystalline material 105 to form a passivation layer 125(e.g., a ruthenium halide, a ruthenium oxyhalide or a ruthenium saltmodified surface layer) in the surface modification step 100. In somecases, the chemical reaction to form the passivation layer 125 may befast and self-limiting. In other words, the reaction product may modifyone or more monolayers of the exposed surface of the polycrystallinematerial 105, but may prevent any further reaction between the surfacemodification solution 115 and the underlying surface. By necessity,neither the polycrystalline material 105 to be etched nor thepassivation layer 125 can be soluble in the surface modificationsolution 115. In some cases, the surface modification step 100 shown inFIG. 1 may continue until the surface reaction is driven to saturation.

After the passivation layer 125 is formed, the substrate may be rinsedwith a first purge solution 135 to remove excess reactants from thesurface of the substrate in a first purge step 130. The purge solution135 should not react with the passivation layer 125 or with the reagentspresent in the surface modification solution 115. In some embodiments,the first purge solution 135 used in the first purge step 130 may usethe same solvent previously used in the surface modification step 100.In other embodiments, a different solvent may be used in the first purgesolution 135. In some embodiments, the first purge step 130 may be longenough to completely remove all excess reactants from the substratesurface.

Once rinsed, a dissolution step 140 is performed to selectively removethe passivation layer 125 from the underlying surface of thepolycrystalline material 105. In the dissolution step 140, thepassivation layer 125 is exposed to a dissolution solution 145 toselectively remove or dissolve passivation layer 125 without removingthe unmodified polycrystalline material 105 underlying the passivationlayer 125. The passivation layer 125 must be soluble in the dissolutionsolution 145, while the unmodified polycrystalline material 105underlying the passivation layer 125 must be insoluble. The solubilityof the passivation layer 125 allows its removal through dissolution intothe bulk dissolution solution 145. In some embodiments, the dissolutionstep 140 may continue until the passivation layer 125 is completelydissolved.

A variety of different dissolution solutions 145 may be used in thedissolution step, depending on the surface modification solution 115used during the surface modification step 100 and/or the passivationlayer 125 formed. In some embodiments, for example, the dissolutionsolution 145 may be an aqueous solution containing a ligand 150, whichassists in the dissolution process. For example, dissolution solution145 may contain a ligand 150 dissolved in an aqueous solution containinga second solvent. The ligand 150 contained within the dissolutionsolution 145 may react or bind with the passivation layer 125 to form asoluble species that dissolves within the second solvent to selectivelyremove the passivation layer 125 from the underlying surface of thepolycrystalline material 105. In some embodiments, the second solventincluded within the dissolution solution 145 may be different from thefirst solvent included within the surface modification solution 115.

Once the passivation layer 125 is dissolved, the ALE etch cycle shown inFIG. 1 may be completed by performing a second purge step 160. Thesecond purge step 160 may be performed by rinsing the surface of thesubstrate with a second purge solution 165, which may be the same ordifferent than the first purge solution 135. In some embodiments, secondpurge solution 165 may use the same solvent (i.e., the second solvent),which was used in the dissolution solution 145. The second purge step160 may generally continue until the dissolution solution 145 and/or thereactants contained with the dissolution solution 145 are completelyremoved from the surface of the substrate.

Wet ALE of ruthenium requires the formation of a self-limitingpassivation layer on the ruthenium surface. The formation of thispassivation layer is accomplished by exposure of the ruthenium surfaceto a first etch solution (i.e., surface modification solution 115) thatenables or causes a chemical reaction between the species in solutionand the ruthenium surface. This passivation layer must be insoluble inthe solution used for its formation, but freely soluble in the secondetch solution (i.e., dissolution solution 145) used for its dissolution.

Although many chemicals can be used to etch ruthenium, thepolycrystalline nature of ruthenium makes it susceptible to pitting ifan etchant preferentially attacks the grain boundaries. Etchantchemistry should, at a minimum, leave the surface no rougher than it wasinitially and ideally improve the surface roughness during etching.Acceptable surface morphology can be accomplished through the formationof a self-limiting passivation layer that is selectively removed in acyclic wet ALE process.

The present disclosure contemplates a wide variety of etch chemistriesthat may be used in the surface modification solution 115 and thedissolution solution 145 when etching ruthenium using the wet ALEprocess shown in FIG. 1 . Example etch chemistries are discussed in moredetail below. Mixing of these solutions leads to a continuous etchprocess, loss of control of the etch and roughening of the pos-etchsurface, all of which undermines the benefits of wet ALE. Thus, purgesteps 130 and 160 are performed in the wet ALE process shown in FIG. 1to prevent direct contact between the surface modification solution 115and the dissolution solution 145 on the substrate surface.

According to one embodiment, the ruthenium surface may be exposed to asurface modification solution 115 including a first solvent containing achlorination agent, which chemically modifies the ruthenium surface toform a ruthenium chloride passivation layer. In one example embodiment,a ruthenium trichloride (RuCl₃) may be used as the passivation layer.For example, a RuCl₃ passivation layer may be formed when the rutheniumsurface is exposed to a solution of trichloroisocyanuric acid (TCCA)dissolved in ethyl acetate (EA). In this embodiment, the TCCA may act asboth the oxidizer and the chlorine source in the reaction. Although TCCAoxidizes the ruthenium surface in the chemical sense to form a rutheniumtrichloride (RuCl₃) passivation layer on the ruthenium surface, nometal-oxide is being formed in the reaction. This differs fromconventional ruthenium etch chemistries, which utilize oxidizing agents(e.g., strong oxidizers) to form a ruthenium metal-oxide passivationlayer.

The chlorine chemistry of ruthenium is very complicated. There are twodistinct crystalline phases of RuCl₃. α-RuCl₃ is almost completelyinsoluble, while β-RuCl₃ is hygroscopic and freely soluble in water,alcohol, and many organic solvents. Additionally, mixed oxychlorides canbe formed when oxygen or water are present during chlorination. Theseoxychlorides tend to be highly soluble. Based on this chemistry, theα-phase of RuCl₃ is considered herein as a preferred passivation layer,in some embodiments. Phase formation, however, is controlled by thereaction conditions.

The self-limiting passivation layer formed during the surfacemodification step 100 must be removed every cycle after its formation. Asecond solution is used in the dissolution step 140 to selectivelydissolve this passivation layer. When TCCA dissolved in EA is used inthe surface modification solution 115 to form α-RuCl₃ on the rutheniumsurface, a pure solvent does not work well in the dissolution step 140because of the difficulty in dissolving α-RuCl₃. Reactive dissolution,however, can be used to effectively remove the ruthenium chloridepassivation layer. In reactive dissolution, ligands 150 dissolved in asecond solvent react with the surface to form a soluble species thatdissolve within the dissolution solution 145. Many different ligandspecies can be used for reactive dissolution of the RuCl₃ passivationlayer. In one embodiment, ethylenediaminetetraacetic acid (EDTA) may beused as the ligand species for reactive dissolution. EDTA reacts withRuCl₃ to form a Ru-EDTA complex that is soluble in aqueous solution.This reaction is base catalyzed, so the dissolution solution 145 mustcontain EDTA and a strong base. Mixing of the TCCA-containing surfacemodification solution 115 and the EDTA-containing dissolution solution145 leads to a continuous etch process, loss of control of the etch, androughening of the surface. Therefore, solvent rinse steps (i.e., purgessteps 130 and 160) are necessary to prevent direct contact between thetwo etch solutions on the ruthenium metal surface.

In the etch chemistry described above, the reactant used for thechlorination of the ruthenium surface is TCCA; however, manychlorination agents will work for this step. Alternative chlorinationagents include, but are not strictly limited to, oxalyl chloride,thionyl chloride and N-chlorosuccinimide. This is not an exhaustive listof all possible chlorination agents that may be used in the surfacemodification step 100. Additionally, other ruthenium halides can also beused as a passivation layer. For example, ruthenium fluoride andruthenium bromide can each be used, in addition to RuCl₃. Theseruthenium halides can be formed using fluorinating agents or brominatingagents, such as but not limited to, 1-Fluoro-2,4,6-trimethylpyridiniumtetrafluoroborate, N-fluorobenzenesulfonimide, N-bromosuccinimide, ordibromoisocyanuric acid.

In the etch chemistry described above, the first solvent used within thesurface modification solution 115 for the chlorination reaction is EA.However, other solvents such as acetone, acetonitrile, and chlorocarbonscan also be used. Again, this is not an exhaustive list of solvents thatcan be used in the surface modification step 100.

In the etch chemistry described above, the dissolution solution 145 isan aqueous solution of EDTA as the ligand 150 and tetramethylammoniumhydroxide ((CH₃)₄NOH) as the base. Alternative ligands for dissolutioninclude, but are not limited to, iminodiacetic acid (IDA),diethylenetriaminepentaacetic acid (DTPA), and acetylacetone (ACAC).EDTA, IDA, and DTPA can be used in aqueous solution, while ACAC can beused in aqueous solution, ethanol, dimethyl sulfoxide (DMSO) or otherorganic solvents. Any strong base can be used in the dissolutionsolution 145. For example, bases such as potassium hydroxide (KOH),sodium hydroxide (NaOH), ammonium hydroxide (NH₄OH), Tetramethylammoniumhydroxide ((CH₃)₄NOH), or any other strong base can be used in thedissolution solution 145 as it is just needed to deprotonate the ligand150 to allow binding with the ruthenium surface.

The ruthenium wet ALE process shown in FIG. 1 and described above uses asolution of trichloroisocyanuric acid (TCCA) in ethyl acetate (EA) toform a self-limiting ruthenium chloride (RuCl₃) passivation layer. Theruthenium chloride passivation layer is then dissolved in an aqueoussolution of ethylenediaminetetraacetic acid (EDTA) at high pH. Thedissolution occurs through a ligand exchange process, where the EDTAreplaces the chloride as a ligand around the ruthenium metal center.Although this dissolution process is slow at room temperature, thekinetics can be improved by dissolving the ruthenium chloridepassivation layer at elevated temperature. In some embodiments, a largeretch amount per cycle can be achieved by running the dissolution at 100°C., as shown in FIG. 2 .

Etching experiments were conducted on coupons cut from a 300 mm siliconwafer with various thicknesses of chemical vapor deposition (CVD)ruthenium deposited on one side. The etch recipe used to etch theruthenium includes multiple wet ALE cycles, where each cycle includes aone minute dip in 5% TCCA dissolved in EA, followed by an EA rinse, a 30second dip in an aqueous solution of 50 mM EDTA and 1 M KOH in H₂O (ordeionized water), a 1 M KOH rinse (or deionized water rinse) and anisopropyl alcohol (IPA) rinse and blow dry. The wet ALE process wasrepeated for a number of ALE cycles under different process conditions:a hot water dissolution, a room temperature (RT) reactive dissolutionand a hot reactive dissolution. The hot dissolutions were performed at100° C.

The total etch amount (nm) as a function of cycle number for the variousetch conditions described above is illustrated in the graph 200 shown inFIG. 2 . Reactive dissolution at room temperature (RT) gives an etchrate of 0.07 nm/cycle. This is much less than a full monolayer ofruthenium and indicates that the dissolution kinetics may be slow atroom temperature. The etch amount per cycle increases substantially(e.g., 0.26 nm/cycle) when the dissolution solution is heated,confirming that the dissolution reaction is kinetically limited. Theetch rate decreased with cycle number and eventually stopped when theexperiment was run using deionized water for dissolution, rather than asolution of EDTA and KOH. This behavior can be explained if thepassivation layer contains a mixture of α-RuCl₃, β-RuCl₃, and variousruthenium oxychlorides (RuO_(x)Cl_(y)). The β-RuCl₃ and RuO_(x)Cl_(y)will be water-soluble while the α-RuCl₃ will remain on the surface. Theamount of α-RuCl₃ on the surface will increase, cycle after cycle, untilthe entire surface is passivated with insoluble α-RuCl₃ and the etchcannot continue. This behavior indicates that ligands 150 in thedissolution solution 145 are beneficial to successful etch behavior.

As shown in FIG. 2 , the dissolution reaction can be optimized and theetch rate can be increased (e.g., from 0.07 nm/cycle to 0.26 nm/cycle)by heating the dissolution solution 145 to an elevated temperature aboveroom temperature. Although the experimental results shown in FIG. 2 wereobtained by heating the dissolution solution 145 to 100° C., thedissolution solution 145 may be heated to any temperature that optimizesthe dissolution reaction and/or produces a desirable etch rate withoutexceeding the boiling point of the dissolution solution 145. Whenutilizing aqueous solutions, the temperature of the dissolution solution145 is limited to 100° C. (the boiling point of water). However, whennon-aqueous solutions are used, the maximum temperature of thedissolution solution 145 may be significantly higher. For example, whenruthenium is etched using ligands dissolved in DMSO, the maximumtemperature of the dissolution solution 145 may be limited to 190° C.(the boiling point of DMSO). Other temperatures may be used for thedissolution solution 145 depending on the polycrystalline material beingetched and the etch chemistry utilized within the dissolution solution145. Regardless of the particular etch chemistry used, the etch amountper cycle is expected to increase monotonically with increasingtemperature until the entire passivation layer 125 is removed or thesolvent boiling point is reached—whichever happens at a lowertemperature.

Although increasing the temperature of the dissolution solution 145 isbeneficial to the dissolution reaction, increased temperatures may beundesirable in the surface modification step. In some cases, the etchchemistries used within the surface modification solution 115 mayrequire the surface modification step 100 to be performed at asubstantially lower temperature. For example, ethyl acetate (EA) boilsat 77° C. When EA is used within the surface modification solution 115,the surface modification solution 115 must be supplied to the substrateat a temperature lower than the boiling point of EA, otherwise solventevaporation may precipitate solute onto the surface. In someembodiments, the surface modification solution 115 shown in FIG. 1 maybe provided to the substrate at (or near) room temperature (e.g., atemperature ranging between 20° C. and 25° C.). Other temperatures maybe used for the surface modification solution 115 depending on thepolycrystalline material being etched and the etch chemistry. In someembodiments, the surface modification solution 115 may be supplied tothe substrate at a temperature, which is less than or equal to roomtemperature. For example, the surface modification solution 115 besupplied to the substrate within a temperature range having a lowerlimit that is set by a freezing point of the surface modificationsolution 115 and an upper limit of 25° C.

The data shown in FIG. 2 was collected using a wet ALE cycle where thechlorination step was performed at room temperature and the dissolutionstep was performed at 100° C. In this case, the desired reactiontemperature for the dissolution of the RuCl₃ passivation layer is abovethe boiling point of ethyl acetate. Because of this, the wet ALE cyclemust be run non-isothermally, or the etch rate must be reduced byreducing the temperature of the dissolution step. In some cases, it maybe beneficial to run the chlorination step at room temperature. Forexample, volatilization of ethyl acetate at elevated temperatures canlead to the precipitation of TCCA on the substrate surface duringprocessing, and any solid TCCA left behind on the surface can lead touncontrolled etching if it mixes with the aqueous ligand exchangesolution. For these reasons, ruthenium wet ALE benefits from being runas a non-isothermal process.

In preferred embodiments of the present disclosure, the wet ALE processshown in FIG. 1 is performed as a non-isothermal process. As noted aboveand shown in FIG. 1 , the wet ALE process described herein may generallyinclude multiple ALE cycles, where each ALE cycle includes a surfacemodification step 100, a first purge step 130, a dissolution step 140and a second purge step 160. In the present disclosure, one or more ofthese processing steps 100, 130, 140 and 160 may be performed at adifferent temperature.

In the present disclosure, thermal cycling is introduced as part of thewet ALE process shown in FIG. 1 by dispensing the liquid solutionsutilized within one or more of the processing steps 100, 130, 140 and160 at a different temperature. The high heat capacity of the liquidsolutions, combined with their high convective heat transfercoefficients, allows the substrate surface to reach thermalequilibration quickly, thus allowing the temperature of the substrate tobe changed within the timescale of a single ALE cycle.

In some embodiments, the wet ALE process shown in FIG. 1 may dispensethe surface modification solution 115 onto a surface of a substrate at afirst temperature (T₁), and may dispense the dissolution solution 145onto the surface of the substrate at a second temperature (T₂), which isdifferent from the first temperature, as depicted in the graph 300 shownin FIG. 3 . The first and second temperatures may be selected toindependently optimize the reactions that occur during the surfacemodification step 100 and the dissolution step 140. In some embodiments,for example, the surface modification solution may be dispensed atapproximately room temperature (e.g., a temperature ranging between 20°C. and 25° C.). However, the dissolution solution may be dispensed at anelevated temperature (e.g., a temperature ranging between 40° C. and190° C.) to optimize the kinetics of the dissolution reaction. Byutilizing liquid solutions having substantially different temperatures,the wet ALE process shown in FIG. 1 provides a cyclic, non-isothermaletch process, which repeatedly adjusts the reaction temperatures of thesurface modification and dissolution steps to independently optimize thesurface modification and dissolution reactions.

As shown in FIG. 1 , purge solutions 135 and 165 may be dispensed ontothe surface of the substrate between the surface modification step 100and the dissolution step 140 to remove the surface modification anddissolution solutions from the surface of the substrate. In someembodiments, the purge solutions 135 and 165 may be utilized to pre-heator pre-cool the substrate prior to performing the next processing step.After performing the surface modification step 100, for example, aheated purge solution 135 may be dispensed onto the surface of thesubstrate. The heated purge solution may be used to adjust or bring thetemperature of the substrate closer to the second temperature (T₂, i.e.,the desired dissolution reaction temperature) prior to performing thenext dissolution step, as shown in FIG. 3 . After the dissolution step140 is performed, a room temperature (or cooled) purge solution 165 maybe dispensed onto the surface of the substrate. The room temperature (orcooled) purge solution 165 may be used to adjust or bring thetemperature of the substrate closer to the first temperature (T₁, i.e.,the desired surface modification reaction temperature) prior toperforming the next surface modification step. By using the temperatureand thermal mass of the purge solutions 135 and 165, the wet ALE processdescribed herein is able to quickly adjust the surface of the substrateto the next process temperature.

According to one embodiment, the cyclic, non-isothermal wet ALE processshown in FIG. 1 for etching a ruthenium surface may include: a) asurface modification step 100 in which the ruthenium surface is exposedto a surface modification solution 115 containing a halogenating agentto chemically modify the ruthenium surface and form a ruthenium halidepassivation layer 125, wherein the surface modification solution 115 isdispensed onto a surface of the substrate at a first temperature; b) afirst purge step 130 in which the substrate is rinsed with a first purgesolution 135 to remove the surface modification solution 115 from thesurface of the substrate; c) a dissolution step 140 in which theruthenium halide passivation layer is exposed to a dissolution solution145 to selectively remove the ruthenium halide passivation layer 125without removing the ruthenium surface underlying the ruthenium halidepassivation layer 125, wherein the second etch solution is dispensedonto the surface of the substrate at a second temperature, which isdifferent from the first temperature; and d) a second purge step 160 inwhich the substrate is rinsed with a second purge solution 165 to removethe dissolution solution 145 from the surface of the substrate. In someembodiments, the steps a)-d) may be repeated for one or more ALE cycles,until a desired amount of the ruthenium material has been removed. It isrecognized that the cyclic, non-isothermal wet ALE process shown in FIG.1 is merely one example of a non-isothermal etch process that may beused to etch a polycrystalline material 105, such as ruthenium.

The ruthenium wet ALE process described above and shown in FIG. 1 relieson both the surface modification and dissolution reactions beingself-limiting. Self-limiting means that only a limited thickness of theruthenium at the surface is modified or removed, regardless of how longa given etch solution is in contact with the ruthenium surface. Theself-limiting reaction can be limited to one or more monolayers ofreaction, or a partial monolayer of reaction.

The ruthenium wet ALE process described above and shown in FIG. 1 can beaccomplished using a variety of techniques. For example, the rutheniumwet ALE process disclosed above may be performed by dipping theruthenium sample in beakers of each etch solution. In this case, purgingcan be accomplished by either rinsing or dipping the sample in anappropriate solvent bath. The ruthenium wet ALE process can also beaccomplished on a spinner. For example, the ruthenium sample may berotated while the etchant solutions are dispensed from a nozzlepositioned above the sample. The rotational motion of the sampledistributes the solution over the surface. After the set exposure time,the nozzle begins dispensing the next solution in the etch recipe. Thisprocess continues through the whole etch cycle and repeats for as manycycles as necessary to remove the desired amount of metal. In someembodiments, solution can also be dispensed onto the backside of thewafer to help control temperature. Deionized (DI) water can be used forthis purpose. For example, hot DI water can be dispensed onto thebackside of the wafer during the dissolution step and room temperatureDI water can be dispensed onto the backside of the wafer during thesurface modification step. For high volume manufacturing, dispensing ofetch solutions and rinses can be executed using conventional tools, suchas wet etching tools and rinse tools.

FIG. 4 illustrates another example of a cyclic, non-isothermal wet ALEprocess in accordance with the present disclosure. More specifically,FIG. 4 illustrates exemplary steps performed during one cycle of anon-isothermal wet ALE process used for etching a polycrystallinematerial 405, such as molybdenum (Mo). In the process shown in FIG. 4 ,a polycrystalline material 405 surrounded by a dielectric material 410is brought in contact with a surface modification solution 415 during asurface modification step 400 to modify exposed surfaces of thepolycrystalline material 405. In one embodiment, the polycrystallinematerial 405 to be etched is molybdenum (Mo). When etching molybdenum,the surface modification solution 415 can contain an oxidation agent 420and a first ligand 425 dissolved in a first solvent.

As shown in FIG. 4 , the oxidation agent 420 oxidizes an exposed surfaceof the polycrystalline material 405 to form a passivation layer 430(e.g., a molybdenum oxide passivation layer) in the surface modificationstep 400. In some cases, the chemical reaction to form the passivationlayer 430 may be fast and self-limiting. In other words, the reactionproduct may modify one or more monolayers of the exposed surface of thepolycrystalline material 405, but may prevent any further reactionbetween the surface modification solution 415 and the underlyingsurface. The first ligand 425 included within the surface modificationsolution 415 reacts with and binds to the passivation layer 430 to forma ligand-metal complex 432, which is insoluble in the first solvent. Insome cases, the surface modification step 400 shown in FIG. 4 maycontinue until the surface reaction is driven to saturation.

After the ligand-metal complex 432 is formed, the substrate may berinsed with a first purge solution 435 to remove excess reactants fromthe surface of the substrate in a first purge step 440. The purgesolution 435 should not react with the ligand-metal complex 432 or withthe reagents present in the surface modification solution 415. In someembodiments, the first purge solution 435 used in the first purge step440 may use the same solvent previously used in the surface modificationstep 400. In other embodiments, a different solvent may be used in thefirst purge solution 435. In some embodiments, the first purge step 440may be long enough to completely remove all excess reactants from thesubstrate surface.

Once rinsed, a dissolution solution 445 is supplied to the substrate toselectively remove the passivation layer 430 from the underlying surfaceof the polycrystalline material 105 in a dissolution step 450. In oneembodiment, the dissolution solution 445 may include a second ligand 455dissolved in a second solvent. When exposed to the dissolution solution445, a ligand exchange process exchanges the first ligand 425 in theligand-metal complex 432 with the second ligand 455 included within thedissolution solution 445 to form a soluble species, which is dissolvedwithin the second solvent to selectively remove the passivation layer430 without removing the unmodified polycrystalline material 105underlying the passivation layer 430. After ligand exchange, thepassivation layer 430 becomes soluble in the dissolution solution 445,which allows for its removal through dissolution into the bulkdissolution solution 445. However, the unmodified polycrystallinematerial 105 underlying the passivation layer 430 must be insoluble inthe dissolution solution 445. In some embodiments, the dissolution step450 may continue until the passivation layer 430 is completelydissolved.

Once the passivation layer 430 is dissolved, the ALE etch cycle shown inFIG. 4 may be completed by performing a second purge step 460. Thesecond purge step 460 may be performed by rinsing the surface of thesubstrate with a second purge solution 465, which may be the same ordifferent than the first purge solution 435. In some embodiments, thesecond purge solution 465 may use the same solvent (i.e., the firstsolvent), which was used in the surface modification solution 415. Thesecond purge step 460 may generally continue until the dissolutionsolution 445 and/or the reactants contained with the dissolutionsolution 445 are completely removed from the surface of the substrate.

The present disclosure contemplates a wide variety of etch chemistriesthat may be used in the surface modification solution 415 and thedissolution solution 445 when etching molybdenum using the wet ALEprocess shown in FIG. 4 . Example etch chemistries are discussed in moredetail below. Mixing of these solutions leads to a continuous etchprocess, loss of control of the etch and roughening of the pos-etchsurface, all of which undermines the benefits of wet ALE. Thus, purgesteps 440 and 460 are performed in the wet ALE process shown in FIG. 4to prevent direct contact between the surface modification solution 415and the dissolution solution 445 on the substrate surface.

In some embodiments, the surface modification solution 415 used foretching the molybdenum surface may include an oxidation agent 420 (suchas, e.g., hydrogen peroxide (H₂O₂), ammonium persulfate ((NH₄)₂S₂O₈),potassium persulfate (K₂S₂O₈), permanganate salts, cerium (IV) salts anddissolved gases, such as nitrogen dioxide (NO₂) and ozone (O₃)) and afirst ligand 425 (e.g., a carboxylate-based ligand, such as oxalic acid,mandelic acid, malic acid, maleic acid or fumaric acid) dissolved in anorganic solvent (such as isopropyl alcohol (IPA) or another alcohol,diethyl ether ((C₂H₅)₂O), acetonitrile (C₂H₃N), dimethyl sulfoxide(C₂H₆OS), a ketone or an acetate). In one example embodiment, themolybdenum surface may be exposed to a surface modification solution 415containing H₂O₂ and oxalic acid dissolved in IPA. In such an embodiment,the hydrogen peroxide (H₂O₂) oxidizes the molybdenum surface to form amolybdenum oxide (MoO₃) passivation layer, which then complexes with theoxalic acid within the surface modification solution 415 to form aligand-metal complex 432 (e.g., an oxymolybdenum oxalate complex), whichis insoluble in the organic solvent.

In some embodiments, the dissolution solution 445 used for etching themolybdenum surface may include a second ligand 455 (e.g., ascorbic acid)dissolved in aqueous solution at high pH (such as, e.g., aqueoushydrochloric acid (HCl), sulfuric acid (H₂SO₄) or another strong acid).Oxymolybdenum oxalate is not soluble in aqueous HCl, but the ascorbateis. When exposed to a dissolution solution 445 containing ascorbic aciddissolved in aqueous HCl, a ligand-exchange mechanism exchanges theoxalic acid in the oxymolybdenum oxalate complex with the ascorbic acidincluded within the dissolution solution to form an oxymolybdenumascorbate, which is dissolved within the aqueous HCl to selectivelyremove the molybdenum oxide passivation layer from the molybdenumsurface.

According to one embodiment, the molybdenum wet ALE process shown inFIG. 4 and described above uses a solution of hydrogen peroxide (H₂O₂)and oxalic acid in IPA to form a self-limiting oxymolybdenum oxalatepassivation layer. The oxymolybdenum oxalate passivation layer is thendissolved in an aqueous solution of a concentrated acid (e.g., HCl,H₂SO₄, other strong acid) containing ascorbic acid. The dissolutionoccurs through a ligand exchange process, where the ascorbic acidreplaces the oxalic acid to form an oxymolybdenum ascorbate passivationlayer. Although this dissolution process is slow at room temperature,the kinetics can be improved by dissolving the oxymolybdenum ascorbatepassivation layer at elevated temperature. In some embodiments, a largeretch amount per cycle can be achieved by running the dissolution at 43°C., as shown in FIG. 6 .

Etching experiments were conducted on coupons cut from a 300 mm siliconwafer with various thicknesses of chemical vapor deposition (CVD)molybdenum deposited on one side. The etch recipe used to etch themolybdenum includes multiple wet ALE cycles, where each cycle includes a10 second dip in 0.1% hydrogen peroxide (H₂O₂)+50 mM oxalic aciddissolved in isopropyl alcohol (IPA), followed by an IPA rinse, a 10second dip in an aqueous solution of 50 M HCl+100 mM ascorbic acid andan IPA rinse. The wet ALE process was repeated for a number of ALEcycles under different process conditions, as shown in FIGS. 5 and 6 .

The graph 500 shown in FIG. 5 illustrates the total etch amount (nm) asa function of time (minutes) for various surface modificationconditions. To obtain the results shown in FIG. 5 , the molybdenumcoupon was soaked in: (a) a surface modification solution containing0.1% H₂O₂+50 mM oxalic acid in IPA at room temperature, (b) a surfacemodification solution containing 0.1% H₂O₂+50 mM oxalic acid in IPA at43° C. and (c) a surface modification solution containing 0.05% H₂O₂+50mM oxalic acid in IPA at 43° C. As shown in FIG. 5 , the oxymolybdenumoxalate formation process is self-limiting at room temperature, but isnot self-limiting at elevated temperatures (e.g., continuous etchprocess re-appears at 43° C.). This limits the maximum temperature forthe surface modification step 400. In some embodiments, the surfacemodification step 400 may be performed at room temperature (or lower) toavoid a continuous etch process.

The thermal activation of hydrogen peroxide-radical initiatedpolymerization relies on the cleaving of peroxide bonds with UV orthermal energy. The graph 500 shown in FIG. 5 further shows that theactivity of hydrogen peroxide may be suppressed with lower peroxideconcentration (e.g., 0.05% H₂O₂). Thus, in some embodiments, it may bepossible to perform the surface modification step 400 at an elevatedtemperature greater than room temperature.

The graph 600 shown in FIG. 6 illustrates the total etch amount (nm) asa function of cycle number for various dissolution conditions. To obtainthe results shown in FIG. 6 , the molybdenum coupon was soaked in: (a) 5M HCL at room temperature, (b) 5 M HCL+100 mM ascorbic acid at roomtemperature and (c) 5 M HCL+100 mM ascorbic acid at 43° C. The graph 600shown in FIG. 6 shows that oxymolybdenum oxalate is not soluble in HCL,however, the ascorbate is. When the molybdenum coupon is exposed to adissolution solution containing 5 M HCL+100 mM ascorbic acid, aligand-exchange mechanism exchanges the oxalic acid in the oxymolybdenumoxalate complex with the ascorbic acid included within the dissolutionsolution to form an oxymolybdenum ascorbate, which is dissolved withinthe aqueous HCl. Thus, the dissolution of the oxymolybdenum oxalate canbe accomplished through ligand exchange where oxymolybdenum ascorbate isthe soluble species.

Reactive dissolution in 5 M HCl+100 mM ascorbic acid at room temperature(RT) gives an etch rate of 0.05 nm/cycle. This is much less than a fullmonolayer of molybdenum and indicates that the dissolution kinetics maybe slow at room temperature. The etch amount per cycle increases (e.g.,0.13 nm/cycle) when the dissolution solution is heated (e.g., to 43°C.), confirming that the dissolution reaction is kinetically limited.The etch rate decreased with cycle number and eventually stopped whenthe experiment was run using only HCl for dissolution, rather than asolution of HCl and ascorbic acid.

As shown in FIG. 6 , the dissolution reaction can be optimized and theetch rate can be increased (e.g., from 0.05 nm/cycle to 0.13 nm/cycle)by heating the dissolution solution 445 to an elevated temperature aboveroom temperature. Although the experimental results shown in FIG. 6 wereobtained by heating the dissolution solution 445 to 43° C., thedissolution solution 445 may be heated to any temperature that optimizesthe dissolution reaction and/or produces a desirable etch rate withoutexceeding the boiling point of the dissolution solution 445. In someembodiments, the dissolution solution 445 shown in FIG. 4 may be heatedto a temperature ranging between approximately 40° C. and 107° C. whenusing a dissolution solution 445 containing 5 M HCL+100 mM ascorbic acidto etch molybdenum. However, the dissolution solution 445 may be heatedto different temperature ranges when other acidic solutions are used toetch molybdenum. For example, the dissolution solution 445 may be heatedto a temperature ranging between 40° C.-337° C. when using pure sulfuricacid (H₂SO₄) or 40° C.-100° C. when using a 1M sulfuric acid solution toetch molybdenum. Other temperatures may be used for the dissolutionsolution 445 depending on the polycrystalline material being etched andthe etch chemistry utilized within the dissolution solution 445.Regardless of the particular etch chemistry used, the etch amount percycle is expected to increase monotonically with increasing temperatureuntil the entire passivation layer 430 is removed or the solvent boilingpoint is reached—whichever happens at a lower temperature.

Like the ruthenium wet ALE process shown in FIG. 1 , the molybdenum wetALE process described above and shown in FIG. 4 relies on both thesurface modification and dissolution reactions being self-limiting.Self-limiting means that only a limited thickness of the molybdenum atthe surface is modified or removed, regardless of how long a given etchsolution is in contact with the molybdenum surface. The self-limitingreaction can be limited to one or more monolayers of reaction, or apartial monolayer of reaction.

In some embodiments, the molybdenum wet ALE process described above andshown in FIG. 4 may require oxidation at low temperature and dissolutionat high temperature. This requires a compromise in the optimization ofthe individual reaction steps, or running as a non-isothermal process toallow for the independent optimization of the surface modification anddissolution reactions.

The molybdenum wet ALE process described above and shown in FIG. 4 canbe accomplished using a variety of techniques. For example, themolybdenum wet ALE process disclosed above may be performed by dippingthe molybdenum sample in beakers of each etch solution. In this case,purging can be accomplished by either rinsing or dipping the sample inan appropriate solvent bath. The molybdenum wet ALE process can also beaccomplished on a spinner. For example, the molybdenum sample may berotated while the etchant solutions are dispensed from a nozzlepositioned above the sample. The rotational motion of the sampledistributes the solution over the surface. After the set exposure time,the nozzle begins dispensing the next solution in the etch recipe. Thisprocess continues through the whole etch cycle and repeats for as manycycles as necessary to remove the desired amount of metal. In someembodiments, solution can also be dispensed onto the backside of thewafer to help control temperature. Deionized (DI) water can be used forthis purpose. For example, hot DI water can be dispensed onto thebackside of the wafer during the dissolution step and room temperatureDI water can be dispensed onto the backside of the wafer during thesurface modification step. For high volume manufacturing, dispensing ofetch solutions and rinses can be executed using conventional tools, suchas wet etching tools and rinse tools.

FIG. 7 illustrates one embodiment of a processing system 700 that mayuse the techniques described herein to etch a polycrystalline material,such as ruthenium, molybdenum, etc., on a surface of a substrate 730. Asshown in FIG. 7 , the processing system 700 includes a process chamber710, which in some embodiments, may be a pressure controlled chamber. Inthe embodiment shown in FIG. 7 , the process chamber 710 is a spinchamber having a spinner 720 (or spin chuck), which is configured tospin or rotate at a rotational speed. A substrate 730 is held on thespinner 720, for example, via electrostatic force or vacuum pressure. Inone example, the substrate 730 may be a semiconductor wafer having apolycrystalline material, such as ruthenium or molybdenum, formed on orwithin the substrate 730.

The processing system 700 shown in FIG. 7 further includes a liquidnozzle 740, which is positioned over the substrate 730 for dispensingvarious etch solutions 742 onto a surface of the substrate 730. The etchsolutions 742 dispensed onto the surface of the substrate 730 maygenerally include a surface modification solution to chemically modifyan exposed surface of the polycrystalline material and form apassivation layer (e.g., a ruthenium halide passivation layer or anoxymolybdenum oxalate passivation layer), and a dissolution solution toselectively remove the passivation layer from the surface of thepolycrystalline material. Purge solutions may also be dispensed onto thesurface of the substrate 730 between surface modification anddissolution steps to separate the surface modification and dissolutionsolutions. Examples of surface modification, dissolution and purgesolutions are discussed above.

As shown in FIG. 7 , the etch solutions 742 may be stored within achemical supply system 746, which may include one or more reservoirs forholding the various etch solutions 742 and a chemical injectionmanifold, which is fluidly coupled to the process chamber 710 via aliquid supply line 744. In operation, the chemical supply system 746 mayselectively apply desired chemicals to the process chamber 710 via theliquid supply line 744 and the liquid nozzle 740 positioned within theprocess chamber 710. Thus, the chemical supply system 746 can be used todispense the etch solutions 742 onto the surface of the substrate 730.The chemical supply system 746, liquid supply line 744 and/or liquidnozzle 740 may be configured to provide heated (and/or cooled) etchsolutions 742 to the substrate. The process chamber 710 may furtherinclude a drain 750 for removing the etch solutions 742 from the processchamber 710.

Components of the processing system 700 can be coupled to, andcontrolled by, a controller 760, which in turn, can be coupled to acorresponding memory storage unit and user interface (not shown).Various processing operations can be executed via the user interface,and various processing recipes and operations can be stored in thememory storage unit. Accordingly, a given substrate 730 can be processedwithin the process chamber 710 in accordance with a particular recipe.In some embodiments, a given substrate 730 can be processed within theprocess chamber 710 in accordance with an etch recipe that utilizes thenon-isothermal wet ALE techniques described herein.

The controller 760 shown in block diagram form in FIG. 7 can beimplemented in a wide variety of manners. In one example, the controller760 may be a computer. In another example, the controller 760 mayinclude one or more programmable integrated circuits that are programmedto provide the functionality described herein. For example, one or moreprocessors (e.g., microprocessor, microcontroller, central processingunit, etc.), programmable logic devices (e.g., complex programmablelogic device (CPLD), field programmable gate array (FPGA), etc.), and/orother programmable integrated circuits can be programmed with softwareor other programming instructions to implement the functionality of aprescribed plasma process recipe. It is further noted that the softwareor other programming instructions can be stored in one or morenon-transitory computer-readable mediums (e.g., memory storage devices,flash memory, dynamic random access memory (DRAM), reprogrammablestorage devices, hard drives, floppy disks, DVDs, CD-ROMs, etc.), andthe software or other programming instructions when executed by theprogrammable integrated circuits cause the programmable integratedcircuits to perform the processes, functions, and/or capabilitiesdescribed herein. Other variations could also be implemented.

As shown in FIG. 7 , the controller 760 may be coupled to variouscomponents of the processing system 700 to receive inputs from, andprovide outputs to, the components. For example, the controller 760 maybe coupled to: the process chamber 710 for controlling the temperatureand/or pressure within the process chamber 710; the spinner 720 forcontrolling the rotational speed of the spinner 720; and the chemicalsupply system 746 for controlling the various etch solutions 742dispensed onto the substrate 730 and/or the temperature of the etchsolutions 742. The controller 760 may control other processing systemcomponents not shown in FIG. 7 , as is known in the art.

In some embodiments, the controller 760 may control the variouscomponents of the processing system 700 in accordance with an etchrecipe that utilizes the non-isothermal wet ALE techniques describedherein. For example, the controller 760 may supply various controlsignals to the chemical supply system 746, which cause the chemicalsupply system 746 to: a) dispense a surface modification solution ontothe surface of the substrate 730 to chemically modify exposed surfacesof the polycrystalline material and create a passivation layer (e.g., aruthenium halide passivation layer or an oxymolybdenum oxalatepassivation layer) on the substrate 730; b) rinse the substrate 730 witha first purge solution to remove excess reactants from the surface; c)dispense a dissolution solution onto the surface of the substrate 730 toselectively remove or dissolve the passivation layer; and d) rinse thesubstrate with a second purge solution to remove the dissolutionsolution from the surface of the substrate 730. In some embodiments, thecontroller 760 may supply the control signals to the chemical supplysystem 746 in a cyclic manner, such that the steps a)-d) are repeatedfor one or more ALE cycles, until a desired amount of thepolycrystalline material has been removed.

The controller 760 may also supply control signals to other processingsystem components. In some embodiments, for example, the controller 760may supply control signals to the spinner 720 and/or the chemical supplysystem 746 to dry the substrate 730 after the second purge step isperformed. In one example, the controller 760 may control the rotationalspeed of the spinner 720, so as to dry the substrate 730 in a spin drystep. In another example, control signals supplied from the controller760 to the chemical supply system 746 may cause a drying agent (such as,e.g., isopropyl alcohol) to be dispensed onto the surface of thesubstrate 730 to further assist in drying the substrate beforeperforming the spin dry step.

In some embodiments, the controller 760 may control the temperature ofthe etch solutions 742 dispensed onto the substrate. Etch solutions canbe dispensed at various temperatures as long as the vapor pressure ofthe liquid is lower than the chamber pressure. For theseimplementations, a spinner with a liquid dispensing nozzle would beplaced in a pressure vessel or a vacuum chamber. The temperature of theliquid being dispensed can be elevated to any temperature below itsboiling point at the pressure of the process. In some embodiments, asurface modification solution may be dispensed onto the surface of thesubstrate 730 at a temperature less than or equal to room temperature(e.g., a temperature less than or equal to 25° C.), and a dissolutionsolution may be dispensed onto the surface of the substrate 730 at anelevated temperature (e.g., a temperature greater than 40° C. and lessthan a boiling point of the dissolution solution). As noted above,higher liquid temperatures can increase the kinetics of dissolution. Insome embodiments, purge solutions may also be utilized to pre-heat orpre-cool the substrate prior to performing the next processing step, asshown in FIG. 3 .

FIGS. 8-9 illustrate exemplary methods that utilize the non-isothermalwet atomic layer etching (ALE) techniques described herein for etchingvarious polycrystalline materials formed on a substrate. It will berecognized that the embodiments of FIGS. 8-9 are merely exemplary andadditional methods may utilize the techniques described herein. Further,additional processing steps may be added to the methods shown in theFIGS. 8-9 as the steps described are not intended to be exclusive.Moreover, the order of the steps is not limited to the order shown inthe figures as different orders may occur and/or various steps may beperformed in combination or at the same time.

FIG. 8 illustrates one embodiment of a method 800 of etching apolycrystalline material using a non-isothermal wet atomic layer etching(ALE) process in accordance with the present disclosure. The method 800shown in FIG. 8 may generally include receiving a substrate having apolycrystalline material formed thereon, wherein a surface of thepolycrystalline material is exposed on a surface of the substrate (instep 810), and dispensing a surface modification solution onto thesurface of the substrate at a first temperature, wherein the surfacemodification solution chemically modifies the surface of thepolycrystalline material to form a passivation layer on the surface ofthe polycrystalline material (in step 820). The passivation layer isself-limited and insoluble to the surface modification solution. Next,the method 800 may include removing the surface modification solutionfrom the surface of the substrate subsequent to forming the passivationlayer (in step 830) and dispensing a dissolution solution onto thesurface of the substrate at a second temperature, which is differentfrom the first temperature (in step 840). The dissolution solutionselectively removes the passivation layer from the surface of thepolycrystalline material in step 840. Next, the method 800 may includeremoving the dissolution solution from the surface of the substrate (instep 850) and repeating the steps of dispensing the surface modificationsolution, removing the surface modification solution, dispensing thedissolution solution, and removing the dissolution solution a number ofALE cycles until a predetermined amount of the polycrystalline materialis removed from the substrate (in step 860).

When utilizing the method 800 shown in FIG. 8 , the first temperatureand the second temperature may be selected so as to independentlyoptimize the reactions that occur during the surface modification anddissolution steps of the non-isothermal wet ALE process. In someembodiments, for example, the surface modification solution may bedispensed (in step 820) at a first temperature, which is less than orapproximately equal to room temperature. In one example, the firsttemperature may be selected from a first temperature range comprising20° C. and 25° C. However, the first temperature is not strictly limitedto such, and may alternatively be selected from a first temperaturerange having an upper limit of approximately 25° C. and a lower limitthat is set by the freezing point of the surface modification solution.In some embodiments, the dissolution solution may be dispensed (in step840) at a second temperature, which is greater than the firsttemperature to optimize the kinetics of the dissolution reaction. Forexample, the dissolution solution may be dispensed in step 840 within asecond temperature range having a lower limit of 40° C. and an upperlimit that is set by the boiling point of the dissolution solution.

In some embodiments, removing the surface modification solution (in step830) may include dispensing a first purge solution onto the surface ofthe substrate to remove the surface modification solution from thesurface of the substrate prior to dispensing the dissolution solution(in step 840). In some embodiments, a temperature of the first purgesolution may bring a temperature of the substrate closer to the secondtemperature before the dissolution solution is dispensed (in step 840).In some embodiments, the temperature of the first purge solution may bewithin 10% of the second temperature.

In some embodiments, removing the dissolution solution (in step 850) mayinclude dispensing a second purge solution onto the surface of thesubstrate to remove the dissolution solution from the surface of thesubstrate before re-dispensing the surface modification solution duringa subsequent ALE cycle. In some embodiments, a temperature of the secondpurge solution may bring a temperature of the substrate closer to thefirst temperature before the surface modification solution isre-dispensed during the subsequent ALE cycle. In some embodiments, thetemperature of the second purge solution may be within 10% of the firsttemperature.

When utilizing the method 800 shown in FIG. 8 , different etchchemistries may be used within the surface modification and thedissolution solutions for etching a wide variety of polycrystallinematerials, such as metals, metal oxides and silicon-based materials.Examples of metals that may be etched using the methods disclosed hereininclude, but are not limited to, ruthenium (Ru), cobalt (Co), copper(Cu), molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), iridium(Ir) and other transition metals. Example of metal oxides that may beetched using the methods disclosed herein include, but are not limitedto, aluminum oxide (Al₂O₃), hafnium oxide (HfO₂). In some embodiments,the methods disclosed herein may also be used to etch silicon-basedmaterials, such as but not limited to, silicon (Si), silicon oxides(e.g., SiO and SiO₂) and silicon nitrides (e.g., Si₃N₄). Althoughvarious examples are provided herein, one skilled in the art wouldrecognize how the methods disclosed herein may be used to etch othermetals, metal oxides and silicon-based materials. Example etchchemistries for etching ruthenium and molybdenum using thenon-isothermal wet ALE techniques disclosed herein are discussed in moredetail below.

In some embodiments, the method 800 shown in FIG. 8 may be used foretching a ruthenium (Ru) surface. When the method 800 is utilized foretching a ruthenium surface, the surface modification solution dispensedin step 820 may include a halogenation agent (e.g., a chlorinationagent, a fluorinating agent or a brominating agent) dissolved in a firstsolvent, and the dissolution solution dispensed in step 840 may includea ligand dissolved in a second solvent. The halogenation agent includedwithin the surface modification solution chemically modifies theruthenium surface to form a halogenated ruthenium passivation layer. Theligand included within the dissolution solution reacts with and binds tothe halogenated ruthenium passivation layer to form a soluble species,which is dissolved within the second solvent to selectively remove thehalogenated ruthenium passivation layer from the ruthenium surface. Insome embodiments, the surface modification solution may be dispensed instep 820 at a first temperature ranging between 20° C. and 25° C. Insome embodiments, the dissolution solution may be dispensed in step 840at an elevated temperature (e.g., a temperature greater than or equal to40° C.) to optimize the kinetics of the dissolution reaction. Forexample, the dissolution solution may be dispensed in step 840 atapproximately 40° C.-100° C. when aqueous dissolution solutions are usedto etch ruthenium.

In other embodiments, the method 800 shown in FIG. 8 may be used foretching a molybdenum (Mo) surface. When the method disclosed herein isutilized for etching a molybdenum surface, the surface modificationsolution dispensed in step 820 may include an oxidation agent and afirst ligand dissolved in a first solvent, and the dissolution solutiondispensed in step 840 may include a second ligand dissolved in a secondsolvent. The oxidation agent oxidizes the molybdenum surface to form amolybdenum oxide passivation layer. The first ligand included within thesurface modification solution reacts with and binds to the molybdenumoxide passivation layer to form a ligand-metal complex, which isinsoluble in the first solvent. When the ligand-metal complex is exposedto the dissolution solution in step 840, a ligand exchange processexchanges the first ligand in the ligand-metal complex with the secondligand included within the dissolution solution to form a solublespecies, which is dissolved within the second solvent to selectivelyremove the molybdenum oxide passivation layer from the molybdenumsurface. In some embodiments, the surface modification solution may bedispensed in step 820 at a first temperature ranging between 20° C. and25° C. In some embodiments, the dissolution solution may be dispensed instep 840 at an elevated temperature (e.g., a temperature greater than orequal to 40° C.) to optimize the kinetics of the dissolution reaction.For example, the dissolution solution may be dispensed in step 840 atapproximately 40° C.-337° C. depending on the acidic solution used toetch molybdenum. In other embodiments, however, the surface modificationsolution and the dissolution solution may each be dispensed atapproximately room temperature.

FIG. 9 illustrates one embodiment of a method 900 that may be used forsubstrate using a non-isothermal wet atomic layer etching (ALE) processin accordance with the present disclosure. The method 900 shown in FIG.10 may generally include: a) receiving the substrate, the substratehaving a ruthenium surface exposed thereon (in step 910); b) exposingthe ruthenium surface to a first etch solution containing a halogenatingagent to chemically modify the ruthenium surface and form a rutheniumhalide passivation layer, wherein the first etch solution is dispensedonto a surface of the substrate at a first temperature (in step 920); c)rinsing the substrate with a first purge solution to remove the firstetch solution from the surface of the substrate (in step 930); d)exposing the ruthenium halide passivation layer to a second etchsolution to selectively remove the ruthenium halide passivation layerwithout removing the ruthenium surface underlying the ruthenium halidepassivation layer, wherein the second etch solution is dispensed ontothe surface of the substrate at a second temperature, which is greaterthan the first temperature (in step 940); e) rinsing the substrate witha second purge solution to remove the second etch solution from thesurface of the substrate (in step 950); and f) repeating steps b)-e) forone or more cycles (in step 960).

In some embodiments, the ruthenium surface may be exposed to the firstetch solution (in step 920) by dispensing the first etch solution onto asurface of the substrate at a first temperature, which is at or nearroom temperature. For example, the first temperature may be selectedfrom a first temperature range comprising 20° C. to 25° C. In someembodiments, the ruthenium halide passivation layer may be exposed tothe second etch solution (in step 940) by dispensing the second etchsolution onto the surface of the substrate at a second temperature,which is greater than the first temperature. For example, the secondtemperature may be selected from a second temperature range comprising40° C. to 100° C. to optimize the kinetics of the dissolution reaction.

In some embodiments of the method 900 shown in FIG. 9 , the first etchsolution may include a chlorination agent dissolved in a first solvent.In such embodiments, the chlorination agent may react with the rutheniumsurface to form a ruthenium chloride passivation layer, which isinsoluble in the first solvent. For example, the chlorination agent mayinclude trichloroisocyanuric acid (TCCA), oxalyl chloride, thionylchloride or N-chlorosuccinimide, and the first solvent may include ethylacetate (EA), acetone, acetonitrile, or a chlorocarbon.

In some embodiments of the method 900 shown in FIG. 9 , the second etchsolution may include a ligand dissolved in a second solvent. In suchembodiments, the ligand may react with and bind to the rutheniumchloride passivation layer to form a soluble species that dissolveswithin the second solvent. For example, the ligand may includeethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA),diethylenetriaminepentaacetic acid (DTPA) or acetylacetone (ACAC), andthe second solvent may include a base.

It is noted that reference throughout this specification to “oneembodiment” or “an embodiment” means that a particular feature,structure, material, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention, butdo not denote that they are present in every embodiment. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarilyreferring to the same embodiment of the invention. Furthermore, theparticular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments. Variousadditional layers and/or structures may be included and/or describedfeatures may be omitted in other embodiments.

The term “substrate” as used herein means and includes a base materialor construction upon which materials are formed. It will be appreciatedthat the substrate may include a single material, a plurality of layersof different materials, a layer or layers having regions of differentmaterials or different structures in them, etc. These materials mayinclude semiconductors, insulators, conductors, or combinations thereof.For example, the substrate may be a semiconductor substrate, a basesemiconductor layer on a supporting structure, a metal electrode or asemiconductor substrate having one or more layers, structures or regionsformed thereon. The substrate may be a conventional silicon substrate orother bulk substrate comprising a layer of semi-conductive material. Asused herein, the term “bulk substrate” means and includes not onlysilicon wafers, but also silicon-on-insulator (“SOI”) substrates, suchas silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”)substrates, epitaxial layers of silicon on a base semiconductorfoundation, and other semiconductor or optoelectronic materials, such assilicon-germanium, germanium, gallium arsenide, gallium nitride, andindium phosphide. The substrate may be doped or undoped.

Systems and methods for processing a substrate are described in variousembodiments. The substrate may include any material portion or structureof a device, particularly a semiconductor or other electronics device,and may, for example, be a base substrate structure, such as asemiconductor substrate or a layer on or overlying a base substratestructure such as a thin film. Thus, substrate is not intended to belimited to any particular base structure, underlying layer or overlyinglayer, patterned or unpatterned, but rather, is contemplated to includeany such layer or base structure, and any combination of layers and/orbase structures.

One skilled in the relevant art will recognize that the variousembodiments may be practiced without one or more of the specificdetails, or with other replacement and/or additional methods, materials,or components. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of various embodiments of the invention. Similarly, for purposesof explanation, specific numbers, materials, and configurations are setforth in order to provide a thorough understanding of the invention.Nevertheless, the invention may be practiced without specific details.Furthermore, it is understood that the various embodiments shown in thefigures are illustrative representations and are not necessarily drawnto scale.

Further modifications and alternative embodiments of the describedsystems and methods will be apparent to those skilled in the art in viewof this description. It will be recognized, therefore, that thedescribed systems and methods are not limited by these examplearrangements. It is to be understood that the forms of the systems andmethods herein shown and described are to be taken as exampleembodiments. Various changes may be made in the implementations. Thus,although the ruthenium wet ALE techniques are described herein withreference to specific embodiments, various modifications and changes canbe made without departing from the scope of the present disclosure.Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense, and such modifications areintended to be included within the scope of the present disclosure.Further, any benefits, advantages, or solutions to problems that aredescribed herein with regard to specific embodiments are not intended tobe construed as a critical, required, or essential feature or element ofany or all the claims.

What is claimed is:
 1. A method for etching a polycrystalline materialusing a non-isothermal wet atomic layer etching (ALE) process, themethod comprising: receiving a substrate having a polycrystallinematerial formed thereon, wherein a surface of the polycrystallinematerial is exposed on a surface of the substrate; dispensing a surfacemodification solution onto the surface of the substrate at a firsttemperature, wherein the surface modification solution chemicallymodifies the surface of the polycrystalline material to form apassivation layer on the surface of the polycrystalline material;removing the surface modification solution from the surface of thesubstrate subsequent to forming the passivation layer; dispensing adissolution solution onto the surface of the substrate at a secondtemperature, which is different from the first temperature, wherein thedissolution solution selectively removes the passivation layer from thesurface of the polycrystalline material; removing the dissolutionsolution from the surface of the substrate; and repeating the steps ofdispensing the surface modification solution, removing the surfacemodification solution, dispensing the dissolution solution, and removingthe dissolution solution a number of ALE cycles until a predeterminedamount of the polycrystalline material is removed from the substrate. 2.The method of claim 1, wherein the first temperature is selected from afirst temperature range having a lower limit that is set by a freezingpoint of the surface modification solution and an upper limit of 25° C.3. The method of claim 1, wherein the first temperature is selected froma first temperature range comprising 20° C. to 25° C.
 4. The method ofclaim 1, wherein the second temperature is greater than the firsttemperature.
 5. The method of claim 1, wherein the second temperature isselected from a second temperature range having a lower limit of 40° C.and an upper limit that is set by a boiling point of the dissolutionsolution.
 6. The method of claim 1, wherein the second temperature isselected from a second temperature range comprising 40° C. to 337° C. 7.The method of claim 1, wherein said removing the surface modificationsolution comprises dispensing a first purge solution onto the surface ofthe substrate to remove the surface modification solution from thesurface of the substrate prior to dispensing the dissolution solution,and wherein a temperature of the first purge solution brings atemperature of the substrate closer to the second temperature before thedissolution solution is dispensed.
 8. The method of claim 7, wherein thetemperature of the first purge solution is within 10% of the secondtemperature.
 9. The method of claim 1, wherein said removing thedissolution solution comprises dispensing a second purge solution ontothe surface of the substrate to remove the dissolution solution from thesurface of the substrate before re-dispensing the surface modificationsolution during a subsequent ALE cycle, and wherein a temperature of thesecond purge solution brings a temperature of the substrate closer tothe first temperature before the surface modification solution isre-dispensed during the subsequent ALE cycle.
 10. The method of claim 9,the temperature of the second purge solution is within 10% of the firsttemperature.
 11. The method of claim 1, wherein the polycrystallinematerial comprises a ruthenium surface, wherein said dispensing thesurface modification solution comprises dispensing a halogenation agentdissolved in a first solvent onto the surface of the substrate at afirst temperature ranging between 20° C. and 25° C., and wherein thehalogenation agent chemically modifies the ruthenium surface to form ahalogenated ruthenium passivation layer.
 12. The method of claim 11,wherein said dispensing the dissolution solution comprises dispensing aligand dissolved in a second solvent onto the surface of the substrateat a second temperature ranging between 40° C. and 100° C., wherein theligand reacts with and binds to the halogenated ruthenium passivationlayer to form a soluble species, which is dissolved within the secondsolvent to selectively remove the halogenated ruthenium passivationlayer from the ruthenium surface.
 13. The method of claim 1, wherein thepolycrystalline material comprises a molybdenum surface, wherein saiddispensing the surface modification solution comprises dispensing anoxidation agent and a first ligand dissolved in a first solvent onto thesurface of the substrate at a first temperature ranging between 20° C.and 25° C., wherein the oxidation agent oxidizes the molybdenum surfaceto form a molybdenum oxide passivation layer, and wherein the firstligand reacts with and binds to the molybdenum oxide passivation layerto form a ligand-metal complex, which is insoluble in the first solvent.14. The method of claim 13, wherein said dispensing the dissolutionsolution comprises dispensing a second ligand dissolved in a secondsolvent onto the surface of the substrate at a second temperatureranging between 40° C. and 337° C., wherein when the ligand-metalcomplex is exposed to the dissolution solution, a ligand exchangeprocess exchanges the first ligand in the ligand-metal complex with thesecond ligand included within the dissolution solution to form a solublespecies, which is dissolved within the second solvent to selectivelyremove the molybdenum oxide passivation layer from the molybdenumsurface.
 15. The method of claim 1, wherein the polycrystalline materialcomprises a transition metal, a transition metal oxide or asilicon-based material.
 16. A method of etching a substrate using anon-isothermal wet atomic layer etching (ALE) process, the methodcomprising: a) receiving the substrate, the substrate having a rutheniumsurface exposed thereon; b) exposing the ruthenium surface to a firstetch solution containing a halogenating agent to chemically modify theruthenium surface and form a ruthenium halide passivation layer, whereinthe first etch solution is dispensed onto a surface of the substrate ata first temperature; c) rinsing the substrate with a first purgesolution to remove the first etch solution from the surface of thesubstrate; d) exposing the ruthenium halide passivation layer to asecond etch solution to selectively remove the ruthenium halidepassivation layer without removing the ruthenium surface underlying theruthenium halide passivation layer, wherein the second etch solution isdispensed onto the surface of the substrate at a second temperature,which is greater than the first temperature; e) rinsing the substratewith a second purge solution to remove the second etch solution from thesurface of the substrate; and f) repeating steps b)-e) for one or morecycles.
 17. The method of claim 16, wherein the first temperature isselected from a temperature range comprising 20° C. to 25° C.
 18. Themethod of claim 16, wherein the second temperature is selected from atemperature range comprising 40° C. to 100° C.
 19. The method of claim16, wherein the first etch solution includes a chlorination agentdissolved in a first solvent, wherein the chlorination agent reacts withthe ruthenium surface to form a ruthenium chloride passivation layer,which is insoluble in the first solvent.
 20. The method of claim 19,wherein the chlorination agent comprises trichloroisocyanuric acid(TCCA), oxalyl chloride, thionyl chloride or N-chlorosuccinimide, andwherein the first solvent comprises ethyl acetate (EA), acetone,acetonitrile, or a chlorocarbon.
 21. The method of claim 19, wherein thesecond etch solution includes a ligand dissolved in a second solvent,wherein the ligand reacts with and binds to the ruthenium chloridepassivation layer to form a soluble species that dissolves within thesecond solvent.
 22. The method of claim 21, wherein the ligand comprisesethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA),diethylenetriaminepentaacetic acid (DTPA) or acetylacetone (ACAC), andwherein the second solvent comprises a base.